1. Field of the Invention
The invention relates to a polymer-based material which comprises a flame-retardant and optionally a plasticiser and further conventionally used additives
2. Brief Description of the Prior Art
Polymers having an aromatic main chain are materials having good properties which are used in many fields. They are high-melting-point materials and for facilitating their processing a quantity of plasticiser is sometimes added or they are mixed with styrene polymers. It is sometimes desired to improve the impact strength of this type of polymers and for that purpose a rubber is often added, for example, EPDM-rubber or rubber-modified polystyrene. In addition additives for other purpose are also used, if so needed. However, a flame-retardant is conventionally incorporated in all materials.
Polymers having an aromatic main chain are to be understood to mean herein polymers the main chain of which is formed from units having at least one aromatic ring, also including hereto-aromatic rings, which is incorporated in the main chain of the polymer. Not included are polymers, for example, polystyrene, the aromatic ring of which is incorporated in the side chain of the polymer.
The polymers of the above-mentioned group have in common that their combustibility and smoke production generally are slightly smaller than those of polymers, for example, polystyrene and the polyalkenes. Of course, the various polymers of this group do differ mutually in their combustibility and smoke production.
For various important applications, for example, in aeroplanes, a great fire resistance and low smoke production are required. For purposes having stringent combustibility requirements it is therefore sometimes to be preferred not to mix a polymer having an aromatic main chain with a modifying polymer which increases the combustibility. In that case it is further to be preferred to use a plasticiser of a predominantly aromatic nature, if such a plasticeser is to be used.
Various possibilities are available to make polymeric materials flame-retardant For example, the quantity of polymer in the material may be reduced by the addition of inorganic fillers. However, large quantities of this material are necessary which would deteriorate the physical properties of the polymers having an aromatic chain to an unacceptable extent. Another possibility consists in mixing with materials which split off water or carbon dioxide during burning, but such materials cannot be used in polymers having high processing temperatures in which most polymers having an aromatic chain are included. Compounds which comprise phosphorus, chlorine and/or bromine, sometimes with an antimony compound, are conventionally used as flame-retardants in polymer materials. Such flame-retardants produce their effect by poisoning of the flame. This results in an incomplete combustion of the polymer, which in turn usually causes an increase of the smoke emission. Furthermore, the thermal stability of these agents is also restricted, so that they are not suitable as such in polymers which require a high processing temperature. Fluorine-containing compounds have seldom been used as flame-retardants. They often are too stable and in addition it has been found that fluorine is not so effective as a flame poison in the vapour phase as is the case with chlorine or bromine.
Another, scarcely examined, possibility is to achieve the flame-retarding effect by an increase of the yield of carbonised material (remaining weight after combustion); this also implies that the emission of combustible gases and hence of smoke is reduced.
It has been found surprisingly that combination of fluorine compounds and boron compounds form good flame-retardants for polymers of this class and this not only for polymer materials of this type which are used in stringent combustibility requirements, but also for combinations which have to satisfy less stringent requirements and the polymer component of which comprises at least 20% polymer having an aromatic main chain.